I don't have any BFL products but have plenty of Ztex boards running on OS X. Note that I use Snow Leopard, not Lion or the previous Leopard.
Both 32-bit and 64-bit compiled jnilib files will work - all you need to do is to install the *legacy* version of the libusb driver using MacPorts, modify the Ztex Makefile in the libusbJava-src folder (this is in the ZTEX SDK, which you'll need to download), and make the jnilib files. Once you've got those... it's really as easy as copying them into the same folder as the version of the pre-compiled Java distribution that Stefan publishes on the Ztex BTCMiner web page.
True, there's a bit of buggering around required to initialise the devices (note - try not to have any iDevices (iPods / iPads / iPhones) on the USB bus at the same time, and ensure your USB hubs are either top-quality or externally powered). But once you've got them initialised, there's nothing else required.
I'm running 5 Ztex boards on OS X 10.6.8 - granted, this is the Mac Pro that I used to develop the OS X version of the libusb Java bridge - but it's fully 64-bit and running the 64-bit jnilib. I simply installed the legacy libusb package from MacPorts on my Dell Mini netbook (running Mac OS X 10.6.0) and copied over the entire folder from the Mac Pro - and this is currently running a 1.15d Ztex development board happily using the 32-bit version of the jnilib.
I went deep into the rabbit hole with the ZTEX SDK (all the way into compiling the FreePascal macro processor and nearly putting my fist through a number of Apple 30" displays at the time... would have been expensive if frustration got the better of me!) - but at the end of the day, it's unnecessary.
All you need to run Ztex FPGAs on OS X Snow Leopard is the old libusb (legacy version), and the jnilib binaries which are OS X specific (since they need an altered Makefile in order to build on OS X).
One thing I *have* found is that Ztex FPGA boards are *incredibly* sensitive to the quality of the USB cables and hubs. With 25 boards to assemble, I obviously needed quite a few USB2.0 hubs, and I wasted a LOT of money buying hubs that the Ztex devices simply refused to work with. Even with massively over-specced power supplies (barrel connectors wired with AWG18 cable to a pair on a gamer PSU's PCIe power plug), I needed to use expensive powered USB hubs to get anything over 4 FPGAs working. The 20-board rig shown above uses three powered 7-port hubs. Stefan's advice in the Wiki about ensuring plenty of ground connections is absolutely critical, but even with a notional 60W supply dedicated entirely to an FPGA board that should only take 11W at max (with a fan)... cheap passive USB hubs simply won't work.
That said, I've taken apart a few of the cheap USB hubs I've received and the internal soldering is beyond appalling. It's a small sample but out of 15 four-port hubs, two had soldering inside that shorted out pins and screwed up everything on that bus. This is perhaps where the 4-chip Ztex boards come into their own - needing fewer USB hubs, at the expense of code incompatibility with other single-Spartan-6 boards (though the Ztex wiki does detail the changes required to support the Quads). I'd be interested in the experiences of other people with substantial numbers of Ztex 1.15x boards and whether USB problems were found...
Anyway I'm flat out at the moment, not on the forums regularly and can't offer a lot of support, but I've written up some of my findings on the Ztex Wiki page re: 'Porting to other platforms'.
And you can get my OS X binaries here - http://www.catfsh.com/bitcoin/fpga/MacOSX-SnowLeopard-Ztex-jnilib-catfish.zip
This folder contains the jnilib files and a couple of shell scripts to initialise and kick off mining, along with the current Ztex JAR. If they don't work, then make sure you've got the legacy libusb installed - use MacPorts and stick to the usual location (/opt/local/lib).
Stefan - if you're reading this and want me to remove the file from my webserver, let me know - it's your code after all.